Seasonal variation of the Sq focus position during 2006–2010

Vichare, Geeta; Rawat, Rahul; Jadhav, M. M.; Sinha, A. K.

doi:10.1016/j.asr.2016.10.009

Cited by 14 publications

(10 citation statements)

References 49 publications

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“…The S q current focus latitude is lowest during September, and it shows a secondary peak in November. These seasonal characteristics are largely consistent with those presented by Vichare et al [] for the Indo‐Russian region. The driving mechanism for the seasonal variation of the S q focus latitude is not well understood.…”

Section: Resultssupporting

confidence: 92%

Quasi‐biennial oscillation of the ionospheric wind dynamo

et al. 2017

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The interannual variation of the ionospheric solar quiet (Sq) current system is examined. A dense magnetometer network over Japan enables the accurate determination of the central position of the northern Sq current loop or the Sq current focus, during 1999–2015. It is found that the Sq focus latitude undergoes an interannual variation of ±2° with a period of approximately 28 months, similar to the quasi‐biennial oscillation (QBO) in the tropical lower stratosphere. The QBO‐like variation of Sq is particularly evident during 2005–2013. No corresponding interannual variability is found in solar extreme ultraviolet radiation. Comparisons with tidal winds, derived from a whole‐atmosphere model, reveal that the QBO‐like variation of the Sq current focus is highly correlated with the amplitude variations of migrating and nonmigrating diurnal tides in the lower thermosphere. The results suggest that the stratospheric QBO can influence the ionospheric wind dynamo through the QBO modulation of tides.

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Section: Resultssupporting

confidence: 92%

Quasi‐biennial oscillation of the ionospheric wind dynamo

et al. 2017

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“…It is to be noted that the peak of the current density (see Figure ) and the magnetic fields (see Figure ) corresponding to normal electrojet are found to be at the same time (∼1030 LT) when the zonal Sq electric field from empirical model (Fejer et al, ) maximizes (see Figure a). Incidentally, the local time corresponding to the monthly mean of Sq focii over the Indian sector during June solstice in solar minimum period was found to be around 1030 LT (Vichare et al, ). However, in afternoon hours, local time corresponding to the peak of CEJ current (∼1630 LT) does not coincide with the time when westward Sq electric field maximizes (∼1730 LT).…”

Section: Discussionmentioning

confidence: 99%

“…An indirect inference of earlier (afternoon) reversal of Sq electric field can be obtained from the magnetic field observations at the focii of Sq current system. Based on geomagnetic field observations using chain of magnetometers during low solar activity (

(〈〉, F 10.7) < 90

sfu) years 2006–2010, Vichare et al () reported that the local time corresponding to monthly mean of focii of Sq current system over the Indian sector during June solstice occurs earlier (∼1030 LT) compared to other seasons. Interestingly, the time of maximum eastward electric field corresponding to vertical drifts over Indian sector reported by Fejer et al () model is also earlier (∼1030 LT) in June solstice compared to other seasons.…”

Section: Discussionmentioning

confidence: 99%

On the Occurrence of Afternoon Counter Electrojet Over Indian Longitudes During June Solstice in Solar Minimum

et al. 2018

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Studies made earlier using ground‐based observations of geomagnetic field over the Indian longitudes revealed that the occurrence of equatorial counter electrojet (CEJ) events in afternoon hours is more frequent during June solstice (May‐June‐July‐August) in solar minimum than in other periods. In general, the June solstice solar minimum CEJ events occur between 1500 local time (LT) and 1800 LT with peak strength of about −10 nT at around 1600 LT. In order to understand the frequent occurrence of these CEJ events, an investigation is carried out using an equatorial electrojet model (Anandarao, 1976, https://doi.org/10.1029/GL003i009p00545) and the empirical vertical drift model by Fejer et al. (2008, https://doi.org/10.1029/2007JA012801). The strength, duration, peak value, and the occurrence time of CEJ obtained using electrojet model match remarkably well with the corresponding observation of average geomagnetic field variations. The occurrence of CEJ is found to be due to solar quiet (Sq) electric field in the westward direction which is manifested as downward drift in Fejer et al. (2008, https://doi.org/10.1029/2007JA012801) model output during 1500–1800 LT. Further, the occurrence of afternoon reversal of Sq electric field in this season is shown to be consistent with earlier studies from Indian sector. Therefore, this investigation provides explicit evidence for the role of westward Sq electric field on the generation of afternoon CEJ during June solstice in solar minimum periods over the Indian sector indicating the global nature of these CEJ events.

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“…The geomagnetic Earth's dipole is also tilted with respect of the ecliptic giving rise to a similar, semiannual behavior in Space Weather parameters as well. Among these parameters are geomagnetic variables like the H component of the magnetic field at the surface of the Earth or the Sq focus location (Vichare et al, 2017), ionospheric parameters like vTEC (Azpilicueta and Brunini, 2011;, and others. The Semiannual Variation (SAV) in all of them is characterized by maximum levels of activity near the equinoxes and minima near solstices.…”

Section: Introductionmentioning

confidence: 99%

Semiannual Variation in radiation belts particle fluxes: Van Allen probes observations

Poblet

Azpilicueta

2018

Preprint

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Abstract. The Semiannual Variation (SAV) is an annual pattern characterized by maxima around the equinoxes and minima near solstices observed in many space weather parameters. Several authors have studied this variation in the electron fluxes of the magnetosphere, focusing only in a few energy levels. In this investigation, Van Allen probes data are processed to extend SAV studies in electron fluxes of a wider energy range. A superposed epoch analysis was applied to data of the REPT and MagEIS instruments obtaining a clear semiannual pattern in the superposed year for L-shell values between 2.5 and 6.5. The Day Of Year (DOY) at which the highest electron flux values are detected near the September equinox coincide with the Russel & McPherron prediction. However, the DOY of the maximum expected close the March equinox occurs with a one month lag from the prediction of the accepted models. In addition, integrating over L-shell the annual DOY-L data with the semiannual pattern resulted in temporal curves that enabled to determine the energy range for which the SAV can be detected: from MeV to tens MeV energy values. Finally, an additional analysis of the fluxes of the Ring Current principal components (H+ and O+ ions) was performed, obtaining no evidence of a SAV on them. This result could indicate that the widely recognized semiannual pattern in the geomagnetic activity is related to a different current system.

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Seasonal variation of the Sq focus position during 2006–2010

Cited by 14 publications

References 49 publications

Quasi‐biennial oscillation of the ionospheric wind dynamo

Quasi‐biennial oscillation of the ionospheric wind dynamo

On the Occurrence of Afternoon Counter Electrojet Over Indian Longitudes During June Solstice in Solar Minimum

Semiannual Variation in radiation belts particle fluxes: Van Allen probes observations

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